Canvasses are frequently stretched over wood frames to provide a medium upon which an artist may render images using oil paint and the like. Over time, the canvas tends to stretch and the wood often tends to shrink, thus reducing the tension of the canvas and permitting it to sag or otherwise become distorted due to wrinkles or depressions formed thereon. As is recognized in the prior art, it is desirable to provide a means for periodically adjusting the tension of the canvas stretched upon a frame. This is typically accomplished by causing adjacent frame members to move apart such that the area enclosed by the frame is increased slightly and consequently the tension of the canvas is likewise increased.
Typically, picture frames are stretched to provide tension to the canvas installed thereupon by driving wedges into the crevices formed between adjacent frame members such that the frame members are forced apart and the area enclosed by the frame is increased. The wedges are inserted from the inside of the frame such that they point toward the outer perimeter of the frame. Such wedges must be tapped into place using a small hammer or mallet and therefore present a hazard to the canvas stretched over the frame. It is possible to inadvertently strike the rear surface of the canvas when attempting to drive the wedges into place. It is also possible to inadvertently drive a wedge through the canvas. Such actions would irreparably damage the canvas and potentially result in the destruction of valuable artwork. The use of such prior art wedges is illustrated in U.S. Pat. No. 1,128,362 issued to Rawbon.
Various alternative mechanisms have also been suggested in the prior art for accomplishing an adjustable tensioning frame. Picture frames having stretcher means for increasing the area of the frame to prevent sagging and distortion of the canvas are well known. One such picture frame is disclosed in U.S. Pat. No. 4,829,685 issued to Persson et al.. The Persson device utilizes first and second eccentric bearing surfaces disposed between adjacent frame members which, when rotated, force the frame members apart. The two bearing surfaces are disposed within cavities or cutouts formed at the interface of the two frame members. The two bearing surfaces cooperate together asymmetrically such that rotation of the two bearing surfaces causes a camming action to force adjacent frame members apart.
A second frame structure utilizing a camming action caused by an eccentric disk is disclosed in U.S. Pat. No. 371,934 issued to Gray. In the Gray device, rotation of an eccentric disk pivotally mounted to one frame member urges the adjacent frame member away. Dowels are used to prevent undesirable rotation of the adjacent frame members. The Gray device utilizes a tool, such as a wrench, to effect rotation of the disk.
Various lever and screw type mechanisms are disclosed in U.S. Pat. Nos. 371,933, 2,149,985, and 3,238,996 issued to Gray, Tepper, and Munn, respectively. The disclosures of Gray, Tepper, and Munn, as well as those of Persson, Gray, and Rawbon provide a broad overview of the various attempts of the prior art to provide means to permit a user to selectively stretch a canvas upon a frame and to periodically make adjustments to the tension of the canvas to compensate for natural stretching of the canvas and/or shrinkage of the frame due to environmental conditions such as humidity and temperature.
Although the prior art has recognized the problem of preventing sagging and distortion of a canvas stretched upon a picture frame, such proposed solutions to date have been ineffective in providing a solution which permits the user to conveniently and safely make such adjustments and which is also inexpensive to manufacture.